Project Summary Universal Test-and-Treat (UTT) could end the HIV epidemic if enough people start and stay on treatment. In 2016, South Africa eliminated CD4 eligibility criteria for antiretroviral therapy (ART) and, in 2017, the country moved to start patients on the same day as diagnosis. These policies were designed to increase ART coverage and have been shown to be effective in clinical trials. However, the real-world effectiveness of these UTT policies at scale is not known. Understanding the impact of UTT and at what stages of the UTT cascade patients are lost will be critical to guide the next phase of South Africa?s HIV response. In collaboration with the National Health Laboratory Service (NHLS), we previously developed a National HIV Cohort by de-duplicating the complete laboratory records of South Africa?s public sector HIV program (>12 million patients at >4000 facilities since 2004). The unique patient identifier that we created and validated enables longitudinal follow-up of all patients nationally from clinical presentation to viral suppression regardless of where they seek care. The cohort is unique in its ability to follow patients who transfer to other facilities without informing their prior clinic. However, it is limited in its ability to assess events that do not include a laboratory test, such as medication pickups. For this proposal, we will update the NHLS National HIV Cohort through the UTT era and link it with data from South Africa?s facility-based ART monitoring and evaluation system. We will use this integrated cohort to quantify losses at each stage of the UTT cascade and to assess systemwide retention and transfer in the UTT era. We will then evaluate the impact of two UTT policies ? eliminating CD4 criteria and implementing same- day ART ? on time from clinical presentation to ART uptake, retention, and viral suppression. South Africa has the largest HIV treatment program in the world. Yet until recently, just half of HIV-infected people in South Africa were virally-suppressed. UTT was South Africa?s largest HIV policy shift since the initial ART rollout in 2004. Our study is innovative because it offers a unique national, longitudinal view of the HIV care cascade in South Africa. Our study is significant because we will determine the extent to which UTT has increased ART coverage and viral suppression and we will identify where in the UTT cascade patients leave care, illuminating opportunities for intervention.